Browsing by Author "Altuntas, H."

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Open Access
Current transport mechanisms in plasma-enhanced atomic layer deposited AlN thin films
(A I P Publishing LLC, 2015) Altuntas, H.; Ozgit Akgun, C.; Donmez, I.; Bıyıklı, Necmi
Here, we report on the current transport mechanisms in AlN thin films deposited at a low temperature (i.e., 200°C) on p-type Si substrates by plasma-enhanced atomic layer deposition. Structural characterization of the deposited AlN was carried out using grazing-incidence X-ray diffraction, revealing polycrystalline films with a wurtzite (hexagonal) structure. Al/AlN/ p-Si metal-insulator-semiconductor (MIS) capacitor structures were fabricated and investigated under negative bias by performing current-voltage measurements. As a function of the applied electric field, different types of current transport mechanisms were observed; i.e., ohmic conduction (15.2-21.5 MV/m), Schottky emission (23.6-39.5 MV/m), Frenkel-Poole emission (63.8-211.8 MV/m), trap-assisted tunneling (226-280 MV/m), and Fowler-Nordheim tunneling (290-447 MV/m). Electrical properties of the insulating AlN layer and the fabricated Al/AlN/p-Si MIS capacitor structure such as dielectric constant, flat-band voltage, effective charge density, and threshold voltage were also determined from the capacitance-voltage measurements.
Open Access
DX-center energy calculation with quantitative mobility spectrum analysis in n-AlGaAs/GaAs structures with low Al content
(ELSEVIER, 2009-03-17) Lisesivdin, S. B.; Altuntas, H.; Yildiz, A.; Kasap, M.; Özbay, Ekmel; Ozcelik, S.
Experimental Hall data that were carried out as a function of temperature (60-350 K) and magnetic field (0-1.4 T) were presented for Si-doped low Al content (x=0.14) n-AlxGa1-xAs/GaAs heterostructures that were grown by molecular beam epitaxy (MBE). A 2-dimensional electron gas (2DEG) conduction channel and a bulk conduction channel were founded after implementing quantitative mobility spectrum analysis (QMSA) on the magnetic field dependent Hall data. An important decrease in 2DEG carrier density was observed with increasing temperature. The relationship between the bulk carriers and 2DEG carriers was investigated with 1D self consistent Schrödinger-Poisson simulations. The decrement in the 2DEG carrier density was related to the DX-center carrier trapping. With the simulation data that are not included in the effects of DX-centers, 17 meV of effective barrier height between AlGaAs/GaAs layers was found for high temperatures (T>300 K). With the QMSA extracted values that are influenced by DX-centers, 166 meV of the DX-center activation energy value were founded at the same temperatures.
Open Access
Effect of film thickness on the electrical properties of AlN films prepared by plasma-enhanced atomic layer deposition
(Institute of Electrical and Electronics Engineers Inc., 2015) Altuntas, H.; Ozgit Akgun, C.; Donmez, I.; Bıyıklı, Necmi
In this paper, AlN thin films with two different thicknesses, i.e., 7 and 47 nm, were deposited at 200 °C on p-type Si substrates by plasma-enhanced atomic layer deposition using trimethylaluminum and ammonia. To investigate the electrical characteristics of these AlN films, MIS capacitor structures were fabricated and characterized using current-voltage and high-frequency (1 MHz) capacitance-voltage measurements. The results showed that the current transport mechanism under accumulation mode is strongly dependent on the applied electric field and thickness of the AlN film. Possible conduction mechanisms were analyzed, and the basic electrical parameters were extracted and compared for AlN thin films with different thicknesses. Compared with 7-nm-thick film, a 47-nm-thick AlN film showed a lower effective charge density and threshold voltage along with a higher dielectric constant.
Open Access
Effect of post-deposition annealing on the electrical properties of B-Ga2O3 thin films grown on p-Si by plasma-enhanced atomic layer deposition
(American Vacuum Society, 2014-08) Altuntas, H.; Donmez, I.; Akgun, C. O.; Bıyıklı, Necmi
Ga2O3 dielectric thin films were deposited on (111)-oriented p-type silicon wafers by plasma-enhanced atomic layer deposition using trimethylgallium and oxygen plasma. Structural analysis of the Ga 2O3 thin films was carried out using grazing-incidence x-ray diffraction. As-deposited films were amorphous. Upon postdeposition annealing at 700, 800, and 900°C for 30min under N2 ambient, films crystallized into β-form monoclinic structure. Electrical properties of the β-Ga2O3 thin films were then investigated by fabricating and characterizing Al/β-Ga2O3/p-Si metal-oxide-semiconductor capacitors. The effect of postdeposition annealing on the leakage current densities, leakage current conduction mechanisms, dielectric constants, flat-band voltages, reverse breakdown voltages, threshold voltages, and effective oxide charges of the capacitors were presented. The effective oxide charges (Qeff) were calculated from the capacitance-voltage (C-V) curves using the flat-band voltage shift and were found as 2.6×1012, 1.9×1012, and 2.5×10 12 cm-2 for samples annealed at 700, 800, and 900°C, respectively. Effective dielectric constants of the films decreased with increasing annealing temperature. This situation was attributed to the formation of an interfacial SiO2 layer during annealing process. Leakage mechanisms in the regions where current increases gradually with voltage were well fitted by the Schottky emission model for films annealed at 700 and 900°C, and by the Frenkel-Poole emission model for film annealed at 800°C. Leakage current density was found to improve with annealing temperature. β-Ga2O3 thin film annealed at 800°C exhibited the highest reverse breakdown field value. © 2014 American Vacuum Society.
Open Access
Electrical characteristics of β-Ga2O3 thin films grown by PEALD
(Elsevier, 2014) Altuntas, H.; Donmez, I.; Ozgit Akgun, C.; Bıyıklı, Necmi
In this work, 7.5 nm Ga2O3 dielectric thin films have been deposited on p-type (1 1 1) silicon wafer using plasma enhanced atomic layer deposition (PEALD) technique. After the deposition, Ga2O 3 thin films were annealed under N2 ambient at 600, 700, and 800 C to obtain β-phase. The structure and microstructure of the β-Ga2O3 thin films was carried out by using grazing-incidence X-ray diffraction (GIXRD). To show effect of annealing temperature on the microstructure of β-Ga2O3 thin films, average crystallite size was obtained from the full width at half maximum (FWHM) of Bragg lines using the Scherrer formula. It was found that crystallite size increased with increasing annealing temperature and changed from 0.8 nm to 9.1 nm with annealing. In order to perform electrical characterization on the deposited films, Al/β-Ga2O3/p-Si metal-oxide- semiconductor (MOS) type Schottky barrier diodes (SBDs) were fabricated using the β-Ga2O3 thin films were annealed at 800 C. The main electrical parameters such as leakage current level, reverse breakdown voltage, series resistance (RS), ideality factor (n), zero-bias barrier height (Bo), and interface states (NSS) were obtained from the current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. The RS values were calculated by using Cheung methods. The energy density distribution profile of the interface states as a function of (ESS-EV) was obtained from the forward bias I-V measurements by taking bias dependence of ideality factor, effective barrier height (e), and RS into account. Also using the Norde function and C-V technique, e values were calculated and cross-checked. Results show that β-Ga2O3 thin films deposited by PEALD technique at low temperatures can be used as oxide layer for MOS devices and electrical properties of these devices are influenced by some important parameters such as NSS, RS, and β-Ga2O3 oxide layer.
Open Access
Electrical conduction and dielectric relaxation properties of AlN thin films grown by hollow-cathode plasma-assisted atomic layer deposition
(Institute of Physics Publishing, 2016) Altuntas, H.; Bayrak, T.; Kizir, S.; Haider, A.; Bıyıklı, Necmi
In this study, aluminum nitride (AlN) thin films were deposited at 200 ï¿½C, on p-type silicon substrates utilizing a capacitively coupled hollow-cathode plasma source integrated atomic layer deposition (ALD) reactor. The structural properties of AlN were characterized by grazing incidence x-ray diffraction, by which we confirmed the hexagonal wurtzite single-phase crystalline structure. The films exhibited an optical band edge around ∼5.7 eV. The refractive index and extinction coefficient of the AlN films were measured via a spectroscopic ellipsometer. In addition, to investigate the electrical conduction mechanisms and dielectric properties, Al/AlN/p-Si metal-insulator-semiconductor capacitor structures were fabricated, and current density-voltage and frequency dependent (7 kHz-5 MHz) dielectric constant measurements (within the strong accumulation region) were performed. A peak of dielectric loss was observed at a frequency of 3 MHz and the Cole-Davidson empirical formula was used to determine the relaxation time. It was concluded that the native point defects such as nitrogen vacancies and DX centers formed with the involvement of Si atoms into the AlN layers might have influenced the electrical conduction and dielectric relaxation properties of the plasma-assisted ALD grown AlN films.